Compound 2a is an inhibitor of human dimethylarginine dimethylaminohydrolase 1 (DDAH1), reported in [1]. However, a lack of selectivity of 2a over NOSs activity, limits its clinical utility. Compound 3a (PubChem CID 11413609) is identified as the most useful human DDAH1 inhibitor in this series as it exhibits little inhibition of NOS enzyme activity.